OPTICAL FIBRE TERMINATION

Abstract: A device for terminating or splicing at least two tubes (12, 13) carrying optical fibres (14, 15) surrounded by reinforcing fibres (17), which device comprises first (1) and second parts (3) which can be secured together during the termination or splicing such that a portion of an optical fibre within each tube extends through aligned apertures in the parts, and such that the reinforcing fibres of each of the tubes are gripped between the secured parts.

Description: Description OPTICAL FIBRE TERMINATION The present invention relates to improvements in connections to optical fibres. Telecommunication systems using optical fibres often employ cables containing large numbers of optical fibres. As the signal path approaches the individual subscriber or a central office or other interface it is necessary to provide connections to individual optical fibres or to groups of fibres. This generally involves separating the fibres and arranging the fibres into an appropriate configuration for connection to another fibre. This arrangement and general handhng of the fibres must be carefully managed to avoid excessive kinking or strain on the fibres or any other damage to the fibres. Nonetheless during their installation and service optical fibres may be exposed to considerable axial forces. For example one method by which a person installing a number of optical fibres can trace the path of any individual fibre, to locate that fibre further on in the bundle, is to pull on the end part of the fibre, and note which fibre moves. Various protection is provided around the optical fibres. For example the optical fibres may be surrounded by one, or several coatings which gives some protection both against physical damage and loss of light, and gives the fibre a certain amount of stiffness. Also optical fibres often run in so-called transportation tubes, which provide additional protection, and still further protection may be provided by additional reinforcing material, in fibrous form, provided between the outer tube and the internal optical fibre. This reinforcement may comprise thin, flexible, high strength fibres e.g. fibres sold under the trade name "Kevlar", which extend longitudinally inside the outer transport tube. Where connections are to be made to the optical fibres it is usual to cut back the outer protection transport tube, and fold away the reinforcing-fibres, so that the inner coated fibres then extend on to the connection apparatus. (Additional short lengths of transport tubes may also be provided around the coated fibres extending from the cut back protection tubes and reinforcing-fibres.) When making connections involving optical fibres it is very important to avoid kinking of the optical fibres, since kinking may result in impaired light transmission, and possibly permanently damage to the fibres. As a result, it is desirable to terminate the cut back protection tube and reinforcing-fibres surrounding the central optical fibre so that any axial pull on the fibre tube is transmitted to the bulkhead or other structure at which the tube is terminated or spliced and not to the fibre contained within the tube. Techniques for splicing or terminating coaxial or other metal cables would not therefore be expected automatically to be suitable for splicing or terminating optical fibre cables. Optical fibres running in transportation tubes are sometimes provided in the form of pigtails, that is generally short lengths of fibre, typically pre-factory-mounted with a connector at one or both ends. The short length pigtails are advantageously used when connecting different parts of a network, rather than connecting the fibres of the different parts of the network directly to each other. The use of pigtails minimises the handling of the main lengths of the optical fibres. It is an object of the present invention to provide an effective means of terminating optical fibres which holds tubes and reinforcing- fibres containing the optical fibres against high axial forces, but which leaves the internal optical fibres unstressed and free to pass on for splicing or termination themselves. In particular, the invention provides for splicing or tem-inating at least two (sometimes two, three, four, or even up to about twelve) optical fibre tubes side-by-side. For example send and return fibres, or a main and a back-up fibre could be spliced or terminated in pairs. The present invention provides a device for terminating or splicing at least two tubes carrying optical fibres surrounded by reinforcing fibres, which device comprises first and second parts which can be secured together during termination or splicing, such that a portion of an optical fibre within each tube extends through aligned apertures in the parts, and such that the reinforcing fibres are gripped between the secured parts. The first and second parts can preferably be mechanically attached to a bulkhead etc. where the tubes are to be terminated, or, for example, to another pair of such parts in the case of a splice. The first and second parts may be provided with mating screw threads, or snap fit parts or the like, to effect the securement together. Where the first and second parts comprise mating screw threads, the parts are preferably made of metal, or polymeric material. Where the parts comprise snap fit mating parts, the parts preferably comprising an electrically insulating material, and are preferably made from polymeric material. Preferably the mating parts are such that re-entry is possible, i.e. it is possible to reopen the screw or snap connection once it has been made. The device advantageously is such that it can be installed and re- entered on site, by the installer, without tools The present invention also provides a method of terminating or splicing at least two tubes carrying optical fibres, each having reinforcing fibres surrounding the optical fibre within the device of the invention, which method comprises: a) removing a portion of the end of each tube so as to expose the optical fibre portion and the reinforcing fibres, b) inserting the optical fibre portion, and the exposed reinforcing fibres of each tube through an aperture in the first of said device parts, c) securing the second of said device parts relative to the first of said parts, such that the optical fibre portions extend through the apertures in the parts and the reinforcing fibres of the optical fibres are gripped between the first and second device parts. The first and second parts are secured relative to each other so that the reinforcing-fibres surrounding the optical fibre are gripped between the parts. To this end the second part is preferably positioned to surround at least part of the first part. As another option the second part may be positioned within the second part. The first and second parts are preferably hollow. They are preferably also generally cylindrical. Where the second part surrounds at least part of the first part, the method preferably also comprises folding back the reinforcing fibres over the outer surface of said first part prior to positioning the second part thereover. One of the said first and second parts, or both is preferably adapted so it can be mechanically attached to a bulkhead etc. where the tubes are to be terminated, or to another pair of such parts in the case of a splice. For some applications, where said second part is secured over said first part, it may be desirable to use a cylindrical part such as a collet in addition to the first and second mating parts. The collet may be placed to extend within the first part over the optical fibre portions and within the reinforcing fibres after the reinforcing fibres have been folded back over the outside of said first part. The second part is then placed over the first part and secured relative thereto. The collet can locate and internally support the reinforcing fibres, provide additional protection for the optical fibre portions. Preferably the collet has an outwardly directed flange at one end which projects over the thickness of the wall of the first part. In this case the collet can also help to position the first part relative to the optical fibres, since its outwardly directed flanges can abut and locate the ends of the tubes surrounding the optical fibres. Where the collet has outwardly directed flanges at one end, these are preferably sufficiently small that the said second part can fit over the collet flanges to engage and be secured to the said first part. When the first and second parts comprise screw threads to secure them together, they are preferably provided with nut portions so enabling the two parts to be screwed together by means of a spanner. Preferably the mating screw threaded surfaces are so disposed that the reinforcing fibres are gripped between them. Preferably only two jacketed optical fibres are connected together. I have surprisingly found that sufficient transfer of axial loads from the reinforcing-fibres surrounding the optical fibres to the first and second parts of the device of the invention (and then to a bulkhead etc) can be achieved without the parts being secured together so tightly that damage occurs. Instead of screw threads or a snap fit other mating surfaces that may be mentioned include interengaging tapering surfaces or bayonet fixings. Such surfaces may be driven by screw threads if desired. In some embodiments according to the invention, where two or more optical fibres are to be terminated side by side the first and second parts contain a single aperture through which both optical fibres (and their respective surrounding tubes and reinforcing fibres pass). In a preferred embodiment according to the invention, one of the first and second parts comprises a projecting portion comprising open channels into which the coated optical fibres, projecting from the cut back transportation tubing, can be positioned. The open channel configuration makes it easy for the installer to view and organise the optical fibres, while the reinforcing-fibres are folded back over the cut back tube and the said first part (or the remaining part of the said first part where the projecting portion projects from the said first part. Embodiments of the invention will now be described with reference to the accompanying drawings in which : Figure 1 is an exploded side view of a device according to the invention; Figure 2 is a cross-sectional side view of the device of Figure 1 in unexploded form; Figure 3 is a side view of the device of Figures 1 and 2 in use. Figures 4 and 5 are perspective views of the first and second parts respectively of a second device according to the invention ; Figures 6 and 7 are sectional views through Figures 4 and 5 respectively; Figure 8 is a sectional view showing the parts of Figures 4 to 7 installed in a bulkhead; Figure 9 is a schematic view showing the passage of optical fibre tubes through the configuration of Figure 8; Figure 10 is a perspective view of a first part of a third device; Figures 11 and 12 are perspective views of a first and second part respectively of another embodiment according to the invention; Figures 13 and 14 are perspective views (Figure 14 being a partly transparent view) of assembled first and second parts of another embodiment according to the invention. Referring now to the drawings, Figure 1 shows a device which comprises a first part 1 for receiving a tube, and fibre reinforced optical fibre, a cylindrical part (collet) 2, and a second part 3. The first part 1 has an internal bore or aperture 4 into which two tubes can be inserted, a head 5 and an externally threaded portion 6. The collet 2 has a diameter such that it can fit within the bore 4 of part 4 but also an outwardly directed flange 7 arranged to project across the wall thickness of part 1 and therefore limit the penetration of the collet into part 1. The second part 3 of the device comprises a nut portion 8 and an elongate portion 9 having a bore 10 therethrough. Nut portion 8 has an internally threaded recess 11 which mates with the external screw threaded part 5 of first part 1. In use the ends of each transportation tube 12, 13 surrounding the fibre reinforced optical fibres are removed to expose the optical fibres 14, 15 (which may be coated or otherwise protected) and the reinforcing fibres 16, 17. The optical fibres 14, 15 and reinforcing fibres 16, 17 are passed through the bore 4 in the first part 1. The reinforcing fibres 16, 17 are then folded back over the externally threaded portion 5 of the first part 1 of the device. The collet 2 is passed into the first part 1 of the device over the optical fibres 14, 15 within the reinforcing fibres 16, 17. It thereby locates the first part 1 relative to the cut back tubes 12, 13, since the ends of the cut back tubes 12, 13 abut against the outwardly directed flange 7 on the collet 2. The second part 3 of the device is then placed over the optical fibres 14, 15 so that they pass through the bore 10. The second part 3 is then screwed down on to the first part 1 of the device, gripping and trapping the reinforcing fibres 16, 17 between the screw thread portions of the first and second parts 1, 3 of the device. Turning now to the second device according to the invention shown in Figures 4 - 9, the first part 21 of the device is shown in Figure 4. It is generally cylindrical in shape but comprises adjacent to each other, an annular ridge 22, groove 24 and collar 26 on its outer surface. These serve together to form an arrangement that can co-operate with a bulkhead (described in detail later). The part 21 also comprises a tube portion 28 extending from the collar 26, and having on its outer surface, part way along its length, a low profile ridge 30._ This provides part of the snap fit mechanism of the device as described later. A cylindrical aperture 32 extends through the entire part 21, for passage in use of optical fibre tubes. Figure 5 shows the second part 33 of the device of the first embodiment. It comprises a cylindrical part 34, having on its internal surface a low profile annular groove 38. Groove 38 is a snap fit with ridge 40 of the first part. The second part 33 also has an aperture 36 extending through its length for passage of the optical fibres and is provided with an end wall 40. Each of the parts 21 and 33 is integrally formed. They are each made from polymeric material, for example a high strength polymer. Polymers that can be used include fluoropolymers, for example "Kevlar"- trade mark). The parts 21 and 33 are preferably moulded. The constituent features of parts 21 and 33 can also be seen in the sectional views (Figures 6 and 7). As shown in these Figures some dimensions of the part are as follows: Figure 6 - Part 21 Diameter "d ', (of aperture 32 in first part 21) 4.5mm Total length "1" (of first part 21) 20.0mm Diameter "d 2 " (inner diameter of collar 26 on part 21) 5.2mm Height "h," (of ridge 30) 0.28 mm Figure 7 - Part 33 diameter d 3 (inner diameter of groove 18) 8.33mm diameter d (inner diameter for entry of part 21) 10.2mm diameter d 5 (exit diameter for optical fibres and reinforcing braids) 4.5mm height hi (height of groove 18) 0.76mm thickness tl (of end wall 40) 1.0 mm The Figures as drawn are approximately four times actual size (unless stated otherwise). Figure 8 shows the part 21 installed in a bulkhead 42. Part 33 is not shown for clarity. The ridge 22 on the part 21 must be sufficiently small to pass through the opening in the bulkhead, and then an additional part 44 is required to engage with the ridge 22 on the inserted side of the bulkhead to retain part 21 in the bulkhead 42. The ridge 42 engages in a snap fit with the additional piece 44, which in turn abuts against the bulkhead 42. Thus the device of this aspect of the invention has two snap fit parts. A first snap fit of the two parts of the device together, and a second snap fit to the bulkhead or the like. This makes for particularly easy installation. Figure 9 shows the position of the device 21 and 33 adjacent a bulkhead 42 with pigtails of optical fibres 44 passing therethrough. A weight 24 (10 kg) is shown to illustrate testing of the installation. Fibres installed in this way can resist a weight of 10 kg without kinking or other damage to the fibres. Figures 10 is a perspective view of a first part of another embodiment of the invention. Like parts are referred to with like reference numerals to the embodiment shown in Figures 4, 6 and 8. This part will co-operate with the same second part 33 shown in Figures 5 and 7, ridge 30' of part 21' snap-fitting with groove 38 of part 33. The major difference between these two embodiments is the shape of ridge 22'. In the embodiment in Figures 10 and 12, part 22' is shorter in one transverse dimension than another. This could be inserted in a bulkhead or the like in any suitable manner. It could for example be inserted through an aperture in the bulkhead that is intermediate in size between the longer and shorter dimensions of part 22', and then simply rotated to retain it in place, with some appropriate locking means to prevent re-rotation. Figure 11 shows the first part of a third embodiment of the invention, and Figure 12 shows co-operating second part of that embodiment. In this case, in place of the ridge 30 on the outer surface the first part engaging a groove 38 in the second part (as shown in earlier Figures), four projecting portions 50, equally spaced around the outer surface first part 21", co-operate with similar spaced apertures 52 in a generally cylindrical second part 33". Again the co-operation is a snap fit. As before the end of the first part 21" distant from the projecting portions 50 may be configured for easy connection to a bulkhead, plate or the like. Again the parts are from the same materials, and preferably made in the same way as the embodiments of the earlier Figures. Referring now to Figures 13 and 14, a first part 21'" fits within, and is a snap fit, with second part 33'". The snap fit is provided by four equally spaced apertures on part 21'" co-operating with four equally spaced projections on the inner surface of surrounding part 33'" (see Figure 14). As before a common aperture (in this case referenced as 58) extends through both parts 21'" and 33'". Two pigtails (with cut back outer tubing) which are to be terminated are passed through aperture 58, and then the reinforcing braids surrounding the fibres themselves are folded back over the outer surface of part 21'", and within part 33'", so that they are trapped between the parts. The pigtails are not shown in the figures for clarity. The pigtails are, of course, inserted, and the reinforcing fibres positioned between parts 21"' and 33'", prior to positioning and snap fitting part 33'" over part 21'". In this embodiment an extra feature is provided on the inner part 21'" in the form of an extending projection 62, extending beyond the end 64 of the common aperture 58 through parts 21'" and 33'". This projection comprises two open channels 66 for receiving respective ones of the fibres from the pair of pigtails, which at this point have been separated from the surrounding reinforcing fibres. The fibres may be coated (with a primary and optionally a secondary coating) in the channels 66, but they are not surrounded by reinforcing fibres. The channels 66 may even be sized to accommodate the fibres in transportation tubes if desired. The channels 66 provide additional support for the fibres. The open configuration of the channels also makes it easy for the installer to sort and organise the fibres relative to each other. In use of the devices of the invention the ends of each tube containing optical fibres are removed to expose the optical fibre (which may be coated or otherwise protected) and the reinforcing fibres. The optical fibres and reinforcing fibres are passed through the apertures in the first of the two parts of the devices (generally indicated as 1 or 21) The reinforcing fibres are then folded back over the first part 1 or 21 and then the second part 13 or 33) is passed over the optical fibres and fitted (e.g. screwed, snap fitted or otherwise) to the first part thereby trapping the reinforcing fibres between the parts 1 or 21 and 13 or 33 of the devices of the invention. Connections made as described above have been found to have a good resistance to axial forces resulting from pulling on the jacket (e.g. testing with a 10 kg weight) but do not result in kinking of the optical fibres. It is surprising that two such tubes can be terminated or spliced in this way since axial pull on the tubes is likely to be laterally off-set from either fibre axis and would be expected to result in unacceptable microbending or other deformation of the fibres. In general, the method of the invention will be used to terminate pairs of tubes at a bulkhead or frame or other part of a cable sphce or sphtter housing. The bulkhead, frame or other part may include a plate having a hole or slot through which the fibres pass and at which the tubes are terminated. The fibres past the plate will then not be stressed by axial pull on the tubes, since that stress will be taken up by the plate.

Claims: CLAIMS 1. A device for terminating or splicing at least two tubes carrying optical fibres surrounded by reinforcing fibres, which device comprises first and second parts which can be secured together during the termination or splicing such that a portion of an optical fibre within each tube extends through aligned apertures in the parts, and such that the reinforcing fibres of each of the tubes are gripped between the secured parts. 2. A device according to Claim 1, wherein the first and second parts are provided with mating screw threads or snap fit parts or equivalents thereof to effect the securement together. 3. A device according to Claim 1 or 2, wherein the parts are detachably secured to each other. 4. A device according to Claim 1 or 3, wherein th& first and second parts are generally hollow and generally cylindrical. 5. A device according to any preceding claim, wherein the first part comprises a projecting portion arranged to extend beyond the mating portions of the parts which grip the reinforcing fibres, projecting portion comprising channels arranged to accommodate the fibres projecting beyond the terminated tubes and reinforcing fibres. 6. A method of terminating or splicing at least two tubes carrying optical fibres, each having reinforcing fibres surrounding the optical fibre within a device according to any preceding claim, the method comprising: a) removing a portion of the end of each tube so as to expose the optical fibre portion and the reinforcing fibres, b) inserting the optical fibre portion, and the exposed reinforcing fibres of each tube through an aperture in the first of said device parts, and c) securing the second of said device parts relative to the first of said parts such that the optical fibre portions extend through the apertures in the parts and the reinforcing fibres of the optical fibres are gripped between the first and second device parts. A method according to claim 5, using a device according to claim 4, which also comprises the step of positioning the fibres in the channels of the projecting portion.

Inventors: VANDERLINDEN MICHEL, VANDERLINDEN, MICHEL
Applicants: RAYCHEM LTD, RAYCHEM SA NV, VANDERLINDEN MICHEL, N.V. RAYCHEM S.A., RAYCHEM LIMITED, VANDERLINDEN, MICHEL
Application year: 1994
Main classification: G02B6
IPC codes: G02B6